Topological scattering singularities and embedded eigenstates for polarization control and sensing applications

TL;DR

This paper explores how topological scattering singularities and embedded eigenstates in epsilon-near-zero materials can be used for advanced polarization control and sensing, revealing new topological phenomena and control mechanisms.

Contribution

It demonstrates that pairs of topologically protected scattering singularities emerge from embedded eigenstates when non-Hermitian parameters are introduced, providing new insights into their topological nature and control.

Findings

Topological charges characterized by integer winding numbers appear as phase vortices.

Charge conservation governs the creation and annihilation of singularities.

Versatile control of reflection amplitude, phase, and polarization is achieved.

Abstract

Epsilon-near-zero and epsilon near-pole materials enable reflective systems supporting a class of symmetry-protected and accidental embedded eigenstates (EE) characterized by a diverging phase-resonance. Here we show that pairs of topologically protected scattering singularities necessarily emerge from EEs when a non-Hermitian parameter is introduced, lifting the degeneracy between oppositely charged singularities. The underlying topological charges are characterized by an integer winding number and appear as phase vortices of the complex reflection coefficient. By creating and annihilating them, we show that these singularities obey charge conservation, and provide versatile control of amplitude, phase and polarization in reflection, with potential applications for polarization control and sensing.